Bridal Wreath spirea can be propagated by green tip cuttings, by woody cuttings, by seeds or by root division. I think the easiest method is root division because the plants tend to have several woody stems growing from the root mass. You should be able to place the blade of a shovel inside the cluster of stems and dig straight down to separate one or more stems from the parent plant. As long as the stems have some roots attached, they should develop into new plants. Or, you can take tip cuttings of 4-6", strip the lower leaves and dip the cut end in rooting hormone. Place the cuttings in moistened seed starting mix, set the pot in a shady area in the yard and keep it watered. The cuttings should root in 3-4 weeks.